Voltage follower for few channels interferes with all channels

[University of Ghent]

In our application we are using voltage followers for a part of the analog input channels. When we decouple the voltage source from its battery supply the channels that go through the voltage follower take up noise, which is normal. But when we connect the battery again and put a voltage on the voltage follower all the analog input channels take up noise. We can solve this by taking the wires, of the channels that go through the voltage follower, out of the pins at the DAQ card and put them back in again. Then all channels acquire voltage in a normal way again.
We are measuring voltages in the differential mode.
Has anyone a solution for this problem?

[RIO-Todd]

Greetings,

Are your signals ground-referenced? If yes, then you will want to make sure you are using a two voltage followers for each channel (one for the signal and the other for the ground). The link below is useful for determining how to connect unity gain buffers within your circuit depending on the different input configurations of your DAQ device.

Using a Unity Gain Buffer (Voltage Follower) with a DAQ Device
http://zone.ni.com/devzone/conceptd.nsf/webmain/CD57A73721E0612586256BAE0055CDD9?opendocument

Just a thought. I hope this helps.

Regards,

Todd D.
NI Applications Engineer

[Erin_B.]

It sounds like the system is actually floating. If so, I would recommend making sure that there is a bias resistor between the negative input and AIGND on the DAQ board, as shown in Fig. 5 of the Voltage Follower article.

Regards,
Erin

[labmaster]

In Figure 5. Voltage Follower for Floating Differential or Nonreferenced Connections of the document,

what's the meaning of the common, gound, and power in a commercial power?

I don't know why the power should connect to the 5V connector on DAQ.

I can't find the ground connector in the commercial power.

(Does it mean the GND of AC power?)